Password changes and spam at same time

In a short period of time ( a month, maybe) I have had a few surprise password changes, and an increase in spam. Since then I have read recent posts in other WP blogs with similar complaints. Coincidence? New version with security holes?

I already know I am quite capable of being superstitious, which is to say I distrust my own superstitions. Nonetheless, I think Sherlock Holmes would consider this coincidence a clue.